1. Field of the Invention
This invention relates to coated glasses having a low sheet resistance, a smooth surface and/or a low thermal emissivity, and more particularly, to a pyrolytic fluorine doped tin oxide coating having a low sheet resistance, e.g. below 14 ohms/square, a smooth outer coating surface, e.g. an outer coating surface roughness of less than 15 nanometers (“nm”) root mean square, and/or a low thermal emissivity.
2. Discussion of the Technology
As is appreciated by those skilled in the coating art, glass sheets are coated to, among other things, provide a coated glass having optical, physical and electrical properties different from the optical, physical and electrical properties of the uncoated glass. By way of illustration and not limiting to the discussion, a pyrolytic chemical vapor deposition (“CVD”) coating of fluorine doped tin oxide deposited on glass provides a coated glass having visible and infrared transmission, percent haze, emissivity, surface roughness, and sheet resistance, e.g. sheet resistance different from the sheet resistance of the uncoated glass sheet.
Unfortunately, altering one set of properties can result in another set of properties to be outside a desired range. For example, and not limiting to the discussion, decreasing the sheet resistance of a fluorine doped tin oxide coating by increasing the coating thickness, e.g. as disclosed in column 3, lines 59-68 of U.S. Pat. No. 3,677,814 (“U.S. Pat. No. '814”) increases the surface roughness. The limitation associated with increasing the surface roughness by increasing the coating thickness can be reduced by increasing the fluoride content of the organic tin composition, e.g. as disclosed in column 4, lines 30-34 of U.S. Pat. No. 3,107,177 (“U.S. Pat. No. '177”). The drawback with this technique is that large additions of fluorine, above a certain level, e.g., ammonium fluoride, are not effective, e.g. as disclosed in column 3, lines 41-53 of U.S. Pat. No. '814 in increasing the conductivity of the coating which reduces the sheet resistance.
As can now be appreciated, it would be advantageous to provide a technique to alter the properties of CVD fluorine doped tin oxide coating to, among other things, decrease sheet resistance with nominal increase in coating thickness; reduce the surface roughness of the coating and/or decrease the thermal emissivity of the coating.